Make sure you're not disconnecting the ipod in iTunes after it's finished updating. If you click the little eject button next to the ipod then windows will unmount the ipod and you won't be able to browse it as a portable drive.
To get at the music make sure you have windows set to allow you to view hidden files. There is a hidden control folder on the ipod and all of the music is stored in there. Unforunately the music is spread across a bunch of folders to make it a pain in the ass to retrieve it, but it can be copied this way.